1. Field of the Invention
This invention relates to the field of orthopedic surgical fasteners for fixation of a soft tissue grafts to a bone tunnel such as would be required in a knee ligament reconstruction.
2. Description of Prior Art
Reconstruction of torn knee ligaments particularly the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) have become commonplace. Tears of knee ligaments can render the knee unstable leading to recurrent episodes of giving way. Reconstruction of these ligaments by using tendon grafts can result in restoration of knee stability and function. To perform a ligament reconstruction, remnants of the torn ligament are removed. Next, bone tunnels are drilled in the femur and tibia at the attachment site for the ligament to be reconstructed. Next, a tissue graft is spanned between the tunnels with the graft ends buried in the bone tunnels. Finally, the graft is tensioned and attached securely to the bone tunnels. The graft then undergoes a slow process of healing which creates a firm attachment of the graft to bone and establishes a new blood supply for the graft. Over a period of 6-18 months the graft remodels to become living tissue which can resist abnormal motions of the knee that would result in giving way.
The fixation of the graft to bone is of paramount importance as any loosening of the graft can result in failure to restore knee stability. Furthermore, early knee motion and exercises which help the patient to recover quickly from surgery can place significant stress on the graft fixation. Adequate stability of graft fixation must be achieved to allow the patient to safely benefit from the effects of early rehabilitation.
Several types of tissue grafts are available for use in knee ligament reconstruction. Each type of graft has certain advantages and disadvantages. The use of autologous hamstring tendons in knee ligament reconstruction has grown in popularity because this graft causes very minimal morbidity to harvest, does not disrupt the extensor mechanism, creates a very strong soft tissue graft and does not expose a patient to the risks of using cadaver tissue. However, fixation of hamstring grafts to the proximal tibial bone tunnel remains a weak link in successful use of the hamstring tendons. The proximal tibia often contains soft bone providing a weak substrate for implant fixation. A second problem is that the tibia is only covered by a thin layer of soft tissue and a prominent implant can often be palpated beneath the skin causing pain. Other types of soft tissue grafts, both of autologous and cadaver tissue, including achilles tendon, quadriceps tendon, fascia lata and palmaris longus tendon are used in certain situations to reconstruct ligaments and again the weak link of fixation to the bone tunnel remains a problem.
A number of devices are known prior art for fixation of soft tissue grafts to bone. However, as will become evident, each of these devices possesses certain disadvantages that limit their successful use.
The first class of devices for soft tissue to bone fixation includes the suture anchors illustrated by U.S. Pat. No. 5,472,452. In his description, Trott discloses a bone anchor which can be placed in a small bone hole and then serves as the attachment sit for soft tissues which are sutured to the bone. Similar type devices are further disclosed by Lee and Sander in U.S. Pat. No. 5,480,403 and by Hayhurst in U.S. Pat. No. 5,601,557. A variation on this device is disclosed by Ross, Snyder, Marchand in U.S. Pat. No. 5,246,441 where a tack is used to secure soft tissues against the bone as it is driven into a small bone hole. None of these devices would be suitable for fixation of knee ligament grafts because of insufficient holding strength.
A second class of fixation devices is illustrated by U.S. Pat. Nos. 4,454,875 and 4,570,623 where metal staples with spikes on the underside are seen securing ligament tissue to bone. These devices are also undesirable in that they have less than ideal fixation strength. They may also by palpable beneath the skin causing pain and necessitating a second operation for their removal. Finally, these devices are difficult to use and reposition and may cause damage to the bone.
A third class of fixation device is the interference screw. An example of this type of implant is the RCI screw.sup.R marketed by Smith-Nephew Endoscopy Corp. The RCI screw.sup.R has blunt threads to avoid damage to a soft tissue graft. This screw is threaded into a bone tunnel along side the strands of a soft tissue graft. The screw compresses the soft tissue graft against the sides of the bone tunnel. Unfortunately, interference screws have poor fixation strength with soft tissue grafts. In addition, the screw occupies part of the bone tunnel leaving less area for healing.
A forth class of fixation device is the screw-washer combination. This consists of standard bone screws used with a washer which is place distal to the bone tunnel. The screw may be tightened down over a soft tissue graft capturing it against the tibia or can act as an anchor around which to tie sutures. The screw-washer is often prominent causing pain and requiring a second operation for implant removal. Graft fixation is weak leaving concerns of graft slippage.
A fifth class of fixation device is a button over which sutures may be tied. Fixation strength is limited by the strength of the sutures and is poor. In some cases the button may be prominent requiring removal.
Other implants such as the Endobutton.RTM. of Smith-Nephew Endoscopy Corp. and various types of threaded pins over which the graft is wrapped are only applicable to fixation of the tendon graft on the femoral side of an ACL reconstruction and thus do not provide a solution to the weak link on the tibial side.
The disadvantages of the available methods of soft tissue fixation can be summarized as:
(a) poor fixation strength allowing slippage of the graft during early rehabilitation; PA1 (b) limited bone to tendon interface for healing; PA1 (c) prominence of the implant which may cause pain; PA1 (d) difficult to adjust fixation; PA1 (e) requirement of second surgery for implant removal; PA1 (f) damage to bone by implant; PA1 (g) implants not amenable to tibia sided graft fixation. PA1 (a) It provides much more secure fixation of the tendon graft to bone. PA1 (b) It allows early aggressive knee rehabilitation due to fixation strength. PA1 (c) It allows for maximal interface between the tendon graft and bone tunnel to maximize the healing surface area. PA1 (d) It lies within the bone tunnel thus avoiding the problems with graft prominence. This reduces the need for a second operation to remove the implant. PA1 (e) It is easily adjustable allowing for intra-operative modification of tendon graft tensioning if necessary. PA1 (f) It stabilizes the graft throughout the bone tunnel preventing graft motion within the bone tunnel which can delay healing and erode bone. PA1 (g) It uniformly compresses the graft against the bone tunnel side walls thus stimulating quicker healing and revascularization of the soft tissue graft. PA1 (h) It can be used with a variety of soft tissue grafts. PA1 (i) It provides for multiple areas of fixation of a soft tissue graft thus relieving high stress concentration on a specific point which can lead to graft failure. PA1 (j) It is easy to manufacture and use.